Influence of powder particle size on microstructure and performance of calcium oxide based ceramic core

A calcium oxide (CaO) based ceramic core used for titanium alloy casting was prepared by injection moulding technology. Through quantitative characterisation and statistical analysis of the microstructure, the influence of powder particle size on the microstructure and properties of the ceramic core was investigated. The results show that, by increasing powder particle size, the size of pores and porosities after sintering were increased with decreased of grain boundary density. Meanwhile, the flexural strength of ceramic core at room temperature was found to decrease with increasing core porosity, and the creep resistance of ceramic core increased with decreasing grain boundary density. The increase in powder particle size of ceramic core is beneficial to reduce linear shrinkage and improve high temperature creep resistance.     

高技术陶瓷产品的精密注射成型制备技术的应用与发展

讨论了陶瓷粉末注射成型制备精密陶瓷部件这一新技术及其国内外发展状况。先进陶瓷精密注射成型的科学基础是现代高分子精密注塑理论和现代陶瓷制造技术,它将高分子流变学、陶瓷粉体技术、陶瓷工艺学和金属模具精密制造技术结合在一起。该技术突出的优点有:①可净近成型各种复杂形状的陶瓷零部件,使烧结后的陶瓷产品无需进行机加工或少加工,从而减少昂贵的陶瓷成本;②成型制品具有极高的尺寸精度和表面光洁度;③可实现微成型(Micro Injection Molding),制备μm-mm范围内的微型陶瓷零件;④成型过程机械化和自动化程度高,重复性好,便于规模化低成本生产。该技术已用于陶瓷发动机、通讯产业中光纤连接器插芯(Ferrule)、计算机工业中光盘盒磁盘驱动用陶瓷轴承和生物医学用陶瓷制品等精密陶瓷件的制造。随着微注射成型新技术的发展,微型陶瓷部件将应用于环境要求苛刻、结构复杂的MEMS系统。     

Net shape CMC components produced by composite flow moulding,pyrolysis and reactive silicon infiltration

This paper describes a novel technique to produce net shape ceramic matrix composites (CMC) artefacts by a modified injection moulding technique called composite flow moulding, (CFM) followed by pyrolysis and reactive silicon infiltration. The peculiarity of the produced components stands in their microstructure which is characterized by fibres crossing the part without interruption. This new method will open the use of CMCs to complex geometries for structural applications because they can be produced to net shape without machining and thus interrupting the fibres.A net shape CMC screw was manufactured, but other shapes, such as: bolts, nuts, rivets, springs and even turbine blades can be easily produced.     

氧化铝陶瓷收缩率的影响因素研究

本文研究了氧化铝粉体的转化率、粒径和晶体形貌对烧结体的收缩性能的影响,结果表明,α-相含量越高,陶瓷收缩率越小;粒度越细,陶瓷收缩率越大;晶体形貌越趋于球形化,陶瓷的轴向收缩率和径向收缩率越接近。     

直接凝固注模成型Si_3N_4及SiC陶瓷──基本原理及工艺过程

直接凝固注模成型（ｄｉｒｅｃｔｃｏａｇｕｌａｔｉｏｎｃａｓｔｉｎｇ，ＤＣＣ）是一种崭新的（准）净尺寸陶瓷成型方法。本文报道了采用此法成型Ｓｉ_３Ｎ_４及ＳｉＣ陶瓷的基本原理和工艺过程。ＤＣＣ成型工艺过程为把高固相含量低粘度的陶瓷浆料浇注到无孔模具中，事先加入到浆料中的生物酶及化学物质通过改变浆料的ｐＨ或电解质浓度来改变浆料的胶体化学行为，从而使浆料原位凝固，得到有足够脱模强度的陶瓷坯体。ＤＣＣ成型的特点为坯体密度高（理论密度的５５％～７０％），坯体均匀，不用或只需少量的有机添加剂（少于１％），可成型大尺寸、复杂形状、高可靠性的陶瓷部件。     

Influence of powder morphology on properties of ceramic injection moulding feedstocks

The powder-binder-mixture is the most critical aspect in the injection moulding processing chain, because the feedstock properties determine the success of the following steps, i.e. excellent flowability in the injecting phase and high green strength during debinding. Therefore, nearly spherical particles which pass each other easily in the feedstock stream are advantageous. The applicable particle size is limited in order to reach high solids loadings which are connected with the specific powder surface. According to this, in this study a very unfavourable powder was introduced into a feedstock. The investigated β-alumina powder consists of plate-like primary particles and has a specific surface of 25 m²/g. During mould filling the particles orient in the feedstock stream which affects the debinding and sintering behaviour and is the source of defects. The influence of the plate-like shape on defect formation is demonstrated in comparison to spherical-shaped particles having the same specific surfaces.     

Effect of powder treatment on injection moulded zirconia ceramics

Agglomerated fine zirconia powder was exposed to dry and wet ball milling and to wet mixing. The subject of study was the effect of powder treatment on the disintegration of agglomerated particles, on the rheological properties of thermoplastic ceramic mixtures, and on the properties of sintered yttria-stabilized tetragonal zirconia polytrystalline ceramics (Y-TZP). Test specimens in the shape of bars and discs were produced by injection moulding of ceramic mixtures containing 52.5 and 49 vol% of powder. The powder treatment was found to yield improved rheological properties of ceramic mixtures and improved mechanical properties of sintered specimens in the case of 52.5 vol% of powder in the ceramic mixture. However, the same or even better mechanical properties of sintered components were found when the loading of ceramic mixture was reduced to 49 vol% of powder and non-treated powder was used.     

Powder-binder separation in injection moulded green parts

For powder injection moulding (PIM) the ceramic powder is mixed with a thermoplastic binder system to achieve an injectable feedstock. In contrast to injection moulding of polymeric components, the binder must be removed after the shaping step before sintering the ceramic part to full density. During the mould filling process shear forces act on the blend that might cause separations of powder particles and binder. In this case polymer films form at the mould surface and at internal interfaces which induce microstructural defects in the debinded part. In particular for multi-component parts this effect is critical since binder films in the joining zone weaken the bonding strength between the two components that might even lead to delamination.For detecting binder separations within the injection moulded bulk material and at joining zones of two-component parts the microstructure of green samples has been studied. Since conventional machining techniques like grinding and polishing modify the original structure, e.g. when particles are pulled out of the matrix and binder smears onto the surface, a special ceramographic method for the preparation of cross-sections was applied. This approach bases on broad ion beam techniques and enables the simultaneous polishing of hard ceramic particles and soft polymer molecules without destroying the structure or producing a relief at the surface. In the analysed samples binder accumulations were found along flow lines, at weld lines, at boundaries of so-called dead water regions and at the interface of two-component parts.     

Analysis of individual and interaction effects of processing parameters on wet grinding performance in ball milling of alumina ceramics using statistical methods

It is of great interest and necessary to closely investigate and understand how ball milling parameters can affect the overall quality of milled ceramic powders. In this paper, we analyzed the individual and interaction effects of the key processing parameters on the wet grinding performance in a ball mill for alumina powder using statistical methods. The grinding performance was evaluated based on three quality characteristics of milled alumina powder: the median particle size (d₅₀), width and skewness reflecting the shape of particle size distributions (PSDs). For this determination, the volume percentage of slurry, solid content, milling speed, milling time, and ball size are regarded as the key parameters affecting these characteristics. Milling experiments were designed by central composite design, and an experimental dataset was collected systematically. The analysis results show that it is worthwhile to consider not only the d₅₀ but also the shape of the PSDs when assessing the ball milling performance. These results are useful for the production of high-quality alumina powders in ceramic industries.     

陶瓷粉体粒径的测量

组成粉体的固体颗粒粒径大小对粉体系统的性质有很大的影响，随着纳米技术的发展，如何更好的表征纳米粉体，最主要的一个参数就是粉体颗粒的大小，而数据的获得需要通过各种测量方法来得到。笔者综述了陶瓷粉体粒径常用的测试方法，并以水热法制备的钛酸钡陶瓷粉体粒径的测定为例讨论了各种测试方法的适用范围及优缺点。     

Fabrication of coloured zirconia ceramics by infiltrating water debound injection moulded green body

Abstract

Abstract

The authors developed a new technique combining ceramic injection moulding and liquid precursor infiltration, presenting a new strategy for fabrication of coloured zirconia ceramics. The authors’ strategy includes ceramic injection moulding 3Y‐TZP powder using a water debinding binder system, debinding moulded parts in water and drying, immersing debound parts in solutions containing different colouring ions and then sintering and creating coloured zirconia ceramics. The fabricated coloured ceramic bars exhibit a core shell structure, and the thickness of the coloured shell can be tailored by adjusting immersion time and temperature. Using solutions containing different colouring ions, ceramic bars with various colours can be prepared.     

The effect of water on the behaviour of alumina–paraffin suspensions for low-pressure injection moulding (LPIM)

The properties of ceramic powder–paraffin suspensions for low-pressure injection moulding (LPIM) is of critical importance to the successful production of high quality ceramic parts. Due to the high hygroscopicity of fine alumina powder, water introduced into the suspension at any stage of the production prior to sintering, may significantly influence its rheological behaviour and hence determine the process parameters as well as the properties of the sintered ceramics. In the industrial environment humidity cannot easily be avoided. Its effect is usually detrimental — it causes flocculation, which is usually the source of defects in sintered ceramics. However, according to the results of the present work, the effect can also be put to good use. Penetration of water into the as-moulded green parts facilitates binder removal and prevents defect formation during this processing step.     

The effect of powder characteristics on pressure sensitivity of powder injection moulding compounds

Pressure effect on the rheological behaviour of powder-polymer compounds intended for powder injection moulding was determined. A single-piston capillary rheometer modified by addition of a second chamber with a restricting needle valve generating backpressure increasing the pressure in the melted material during the flow through the die was employed to determine pressure sensitivity coefficients. The results obtained for three compounds varying in the characteristics of powders used confirmed that compounds at the loading level close to the maximum packing are more sensitive to pressure than polymer binder. It is shown that pressure sensitivity coefficients of these materials are strongly dependent on powder characteristics — particle size and particle size distribution. The highest coefficient (32.9 GPa⁻¹) was found for compound containing broad particle size distributed powder having a perceptible portion of small particles.     

Fused deposition modeling of mullite structures from a preceramic polymer and γ-alumina

Thermoplastic filaments for Fused Deposition Modeling fabrication of mullite ceramic components were produced from a polymethylsiloxane ceramic precursor, γ-Al₂O₃ powder and ethylene vinyl acetate (EVA) as an organic, elastomeric binder. Two micron-sized γ-Al₂O₃ powders with different particle size distributions were used. Both type of powders could be successfully 3D printed, however γ-Al₂O₃ with finer particle size resulted in better quality of printed parts with much smoother surface.Sintering experiments showed that mullite starts forming already at 1250 °C, but a final sintering of 1550 °C is necessary to achieve pure mullite using the coarse powder, while some residual α-Al₂O₃ was present when using finer powder.Results demostrate that Fused Deposition Modeling can be used to shape preceramic polymers to generate large scale components with a complex shape in which, during firing, the siloxane produces highly reactive silica that allows for the in-situ formation of silicate ceramic phases, such as mullite.     

Effect of electromelted corundum crystal size and shape on the microstructure and permeability of porous ceramic

The effect of electrocorundum powder particle size and shape on its properties are studied. Results are presented for a study of the microstructure and permeability of porous ceramic based on electrocorundum with different particle sizes and shapes. The effect of production factors, and also air flow rate and the thickness of ceramic specimens on the air pressure drop ahead and after a specimen and the gas permeability coefficient are studied.     

Differential sintering in ceramic injection moulding: particle orientation effects

The sintering shrinkage in three orthogonal directions was measured in sections cut from large rectangular injection moulded ceramic blocks. Two powders were used: a comminuted alumina and a chemically-derived zirconia. Pronounced anisotropy of shrinkage was observed in the former whereas the equiaxed zirconia showed uniform shrinkage throughout the moulding. The pattern of shrinkage anisotropy was consistent with that observed by other investigators and indicates that slight particle anisotropy can introduce differential sintering. The sintering shrinkage in the alumina powder was found to be most pronounced perpendicular to the main flow direction.     

Elaboration of PIM feedstocks with 316L fine stainless steel powders for the processing of micro-components

The paper is concerned with the way to prepare feedstocks for powder injection moulding of fine stainless steel powders. The way to prepare adequate feedstocks is described, and injection moulding experiments are determined. The effects of powder volume loading, as well as mixing conditions are investigated and the results indicate that powder loading, injection moulding conditions and sintering kinetics largely influence the resulting shrinkage after sintering. Finally, the modelling and associated numerical simulations are used the help process design.     

Effect of salt species on characterization of Bi3NbTiO9 powders prepared by molten salt method

The carbonates, chloride and sulphate salts were chosen as fluxes to synthesize Bi₃NbTiO₉ (BNTO) powders at low temperature by the molten salt synthesis (MSS) method and the influence of salt species on the formation and powder characteristics of BNTO was investigated in this paper. The results showed that for the sulphate flux the formed particle size was the largest among all the used salts, but the fastest particle growth rate was found in the carbonates flux. Investigations on morphology characteristics of powders showed the plate-like powders with smaller particle size were synthesized in the chloride flux, but the powders obtained in the sulphate flux were shown to be irregular blocks in shape. Further studies indicated the salt content had a strong influence on crystallization of BNTO from the chloride flux.     

Study of the morphology and granulometry of polyethylene–clay nanocomposite powders

Medium‐density polyethylene (MDPE) matrix nanocomposites reinforced with different clay contents were produced by using a planetary ball mill. The morphology of all the milled samples, including pure polyethylene and the polyethylene–clay nanocomposites, was examined by scanning electron microscopy. To investigate the effects of milling time and clay content on the particle size of polyethylene powder, sieve analysis was used. The results showed that during milling, the regular shape of pure polyethylene powder converts into flake shapes and the average particle size of the powder increases upon increasing the milling time because the welding mechanism is predominant. Also, the presence of the clay can increase the maximum‐particle size, and increasing the clay content can decrease the milling time required to reach the same maximum particle size. J. VINYL ADDIT. TECHNOL., 2010. © 2009 Society of Plastics Engineers